@audio/stretch-pghi
Phase Gradient Heap Integration vocoder — "Phase Vocoder Done Right" (Průša & Holighaus, 2017), causal RTPGHI variant. Synthesis phase is integrated from the analysis phase gradients (instantaneous frequency across time, stretched group delay across frequency), visiting bins in order of decreasing magnitude via a max-heap — phase always flows from strong bins into their neighbourhoods.
No peak picking, no transient heuristics: chirps, vibrato and dense spectra stay coherent by construction.
import pghi from '@audio/stretch-pghi'
let out = pghi(data, { factor: 2 })
| Param | Default | |
|---|---|---|
factor | 1 | Time stretch ratio |
frameSize | 2048 | FFT size (power of 2) |
hopSize | frameSize/8 | Hop — gradient integration wants denser frames than peak locking |
tolerance | 1e-6 | Bins below tolerance×max get random phase |
Sliding stretch: factor may be a function t => ratio of source time in seconds, read at every analysis frame. pghi(data, { factor: t => t < 5 ? 1 : 2, sampleRate: 48000 }) keeps the first 5 s as is and plays the rest at half speed; sampleRate (default 44100) converts frame positions to t.
Use when: modulated material — vibrato, glides, chirps, pitch-unstable sources (measured: beats @audio/stretch-pvoc-lock on tones/glissandi, ~4× better than plain pvoc on sweeps).
Not for: steady polyphony — identity phase locking reproduces exact intra-region phase relations that first-order gradient integration only approximates; use @audio/stretch-pvoc-lock there.
Part of @audio/stretch.